PHYTOPLANKTON OF THE VARIOUS SIZE GROUPS OF THE NORTH-WEST PART OF PACIFIC-OCEAN DURING SUMMER SEASON

Material was collected during the 22 th cruise of R/V ''Akademik M. Ke ldyish'' in the North-west part of the Pacific ocean in July - August 1991. Picophytoplankton mainly consisting of cyanobacteria (up to 90%) comprised from 70 to 90% of the total phytoplankton abundance. Nanoph ytoplankton was mainly made up from small phytoflagellates (2 - 4 mkm) , cryptomonades and coccolitoforides such as Emiliania huxley. Nanophy toplankton had substantial part in the total biomass (22 - 87%). Summe r species such as Neodenticula seminae prevaluated among large phytopl ankton. The spatial and vertical changes in the phytoplankton communit ies have described. The taxonomic composition and vertical distributio n depended upon the nutrients concentration in the upper mixed layer.